At X-ray wavelengths, shell-type SNRs may show emission from either or both of the forward-shocked ISM/CSM and the reverse-shocked ejecta, depending on the evolutionary state of the remnant. The physical processes causing the X-ray emission can be either thermal, non-thermal, or both. The thermal emission is generally a combination of both Bremmsstrahlung continuum produced when hot ions and electrons interact, as well as line emission from highly-ionized atoms of various metals, such as O, Fe, Ne, Si, and S. Nonthermal emission in SNRs arises from synchrotron emission identical to that seen in radio waves, but from much more energetic (\(\sim 10-100\)  TeV) electrons. Because electrons can only be accelerated to energies this high very close to the blast wave, synchrotron emission is most often seen from the outer edges of the shell in shell-type SNRs [1]}, [2]}.
